Equilibrium state- When rate of formation of a product in a process is in competition with rate of formation of reactants , the state is then named as “ Equilibrium state ”
Equilibrium in physical processes : H2O ( s ) ⇌ H2O ( l ) ⇌ H2O ( vap )
Law of chemical equilibrium : solid ⇌ liquid ⇌ gas
At a given temperature , the product of concentrations of the reaction products raised to the respective stoichiometric coefficient in the balanced chemical equation divided by the product of concentrations of the reactants raised to their individual stoichiometric coefficients has a constant value . This is known as the Equilibrium Law or Law of Chemical Equilibrium .
aA + bB⇌cC + dD
Kc =[ C ] c [ D ] d /[ A ] a [ B ] b
Chemical equation |
Equilibrium constant |
aA + b B⇌c C + D |
K |
cC + d D⇌a A + b B |
K ′ c =( 1 / Kc ) |
na A + nb B ⇌ncC + ndD |
K ′″ c = ( Kc n ) |
Concentrations or partial pressure of pure solids or liquids do not appear in the expression of the equilibrium constant . In the reaction ,
Ag2O ( s ) + 2HNO3 ( aq ) ⇌ 2AgNO3 ( aq ) + H2O ( l ) If Qc > Kc , the reaction will proceed in the direction of reactants ( reverse reaction ).
If Qc < Kc , the reaction will proceed in the direction of the products ( forward reaction )
Kp is equilibrium constant in terms of partial pressure of gaseous reactants and products .
Kc is equilibrium constant in terms of molar concentration of gaseous reactants and products .
Kp = Kc ( RT ) ∆n here R is gas constant , T is temperature at which the process is carried out & ∆n is no . of moles of gaseous product minus no . of moles of gaseous reactants .
If Kc > 10 3 ; Kc is very high i . e . the reaction proceeds nearly to completion . If Kc < 10 3 ; Kc is very small i . e . the reaction proceeds rarely .